This indicates an attack attempt against a Denial of Service vulnerability in Adobe Reader.
The vulnerability is caused by an error when the vulnerable software handles a malicious ".pdf" file. A remote attacker may be able to exploit this to cause a denial of service condition on an affected system.
Adobe Reader XI (11.0.03) and prior 11.x versions
Adobe Reader X (10.1.7) and prior 10.x versions
Adobe Acrobat XI (11.0.03) and prior 11.x versions
Adobe Acrobat X (10.1.7) and prior 10.x versions
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.